Congestive heart failure (CHF) is a condition in which the blood pumping function of the heart is inadequate to meet the needs of body tissue. CHF is one of the most common causes of hospitalization and mortality in Western society.
CHF results from a weakening or stiffening of the heart muscle most commonly caused by myocardial ischemia (due to, for example, myocardial infarction) or cardiomyopathy (e.g. myocarditis, amyloidosis). Such weakening or stiffening leads to reduced cardiac output, an increase in cardiac filling pressures, and fluid accumulation. Congestive heart failure (CHF) is generally classified as systolic heart failure (SHF) or diastolic heart failure (DHF).
In SHF, the pumping action of the heart is reduced or weakened. A common clinical measurement is the ejection fraction (EF) which is a function of the volume of blood ejected out of the left ventricle (stroke volume), divided by the maximum volume remaining in the left ventricle at the end of diastole or relaxation phase. A normal ejection fraction is greater than 50%. Systolic heart failure has a decreased ejection fraction of less than 50%. A patient with SHF may usually have a larger left ventricle because of phenomena called cardiac remodeling aimed to maintain adequate stroke-volume. This pathophysiological mechanism is associated with increased atrial pressure and left ventricular filling pressure.
In DHF, the heart can contract normally but is stiff, or less compliant, when it is relaxing and filling with blood. This impedes blood filling into the heart and produces backup into the lungs resulting in pulmonary venous hypertension and lung edema. Diastolic heart failure is more common in patients older than 75 years, especially in women with high blood pressure. In diastolic heart failure, the ejection fraction is normal.
CHF can be managed via a pharmacological approach which utilizes vasodilators for reducing the workload of the heart by reducing systemic vascular resistance and/or diuretics which prevent fluid accumulation and edema formation, and reduce cardiac filling pressure.
In more severe cases of CHF, assist devices, such as mechanical pumps can be used to reduce the load on the heart by performing all or part of the pumping function normally done by the heart. Temporary assist devices and intra-aortic balloons may be helpful. Cardiac transplantation and chronic left ventricular assist device (LVAD) implants may often be used as last resort. However, all the assist devices currently used are intended for improving pumping capacity of the heart and increasing cardiac output to levels compatible with normal life and are typically used to sustain the patient while a donor heart for transplantation becomes available. There are also a number of pacing devices used to treat CHF. Mechanical devices enable propulsion of significant amounts of blood (liters/min) but are limited by a need for a power supply, relatively large pumps and possibility of hemolysis and infection are all of concern.
Surgical approaches such as dynamic cardiomyoplasty or the Batista partial left ventriculectomy are used in severe cases, as is heart transplantation, although the latter is highly invasive and limited by the availability of donor hearts.
Although present treatment approaches can be used to manage CHF, there remains a need for a device for treating CHF which is devoid of the above described limitations of prior art devices.